1. Field of the Invention
This invention relates to the presentation of fasteners to workpieces. More specifically, it relates to fasteners which are to be machine applied and need to be fed, through a delivery tube, from a supply, such as a carrier tape, to a remote workpiece--often with restricted access.
2. Description of the Prior Art
It has been found desirable to provide such a delivery tube with the capability of exerting a controlled restraining force, sufficient to hold the fasteners in a desired orientation throughout their passage through the tube--but preferably without marking the fastener body.
The term tube is used herein to embrace any configuration or disposition of chamber, enclosure or passageway.
The term fastener is used herein to embrace a disparate variety of elements for joining one component to a another.
Of the generality of fasteners, the invention is particularly, but not exclusively, concerned with rivets--for example hollow, tubular, self-piercing rivets, with a shank and relatively enlarged head.
Fasteners, such as rivets, which are short (along their fastening axis) in relation to their girth, present special handling and delivery problems--not least because of their innate tendency to tumble, or lose their axial orientation with respect to the direction of (delivery) movement.
A typical applicator for applying fasteners consists of a hydraulic cylinder carrying a fastener driving plunger mounted on a `C`--frame.
Fasteners, carried in a tape, are fed in synchronism with the cylinder operation, and are guided over the workpiece through a replaceable nozzle.
Diverse mechanisms have been developed previously to ensure that machine applied fasteners arrive at the workpiece in the correct orientation.
Where it is possible to introduce a guidance tool (as in the case of, say, spring pilot anvils, which are used to guide semi-tubular rivets into position), or where the fastener has adequate bearing surfaces along its major diameter, the guidance is generally not unduly problematic.
However, where it is not possible to introduce a guidance tool and where the contact or bearing surface is limited (as for instance with a fastener with a countersunk head), or where the length of the fastener is small relative to its (head) diameter, the problems of ensuring accurate presentation are more acute.
This is particularly so where the application requirements are such that the delivery tube cannot be maintained in a vertical orientation--i.e. absent reliance upon a gravity feed.